What are "weak squares"?

One concept that new players sometimes find difficult to grasp is weak squares. “I understand how a piece can be weak, but a weak square? What does that mean?”

A square is weak when it is controlled by your opponent and you have little or no chance of regaining control due to a lack of pieces which can effectively fight for that square. Typically, pawns that could have controlled the square have moved past it and, of course, cannot move backwards to help guard it. Single weak squares are called “holes”. Holes on the opponents half of the board that can be occupied by one of your supported pieces are called “outposts”.

Sometimes, number of adjacent squares of the same color can become weak. This often happens when a bishop of that color gets captured and the remaining pawns are mostly on squares of the other color. When this situation occurs, the weakened squares are called a “weak square complex”. A typical weak square complex occurs after a fiachettoed bishop (say it was on g7—a black square) gets captured. The remaining pawns are on f7, g6, and h7—all white squares. Now nothing is defending the squares f6, g7, h6 (and perhaps even f8 and h8). Or maybe only the Black king is defending them. That is not a good situation, especially if White still has his black-squared bishop and queen.

Occasionally, as in the two games presented below, all of the squares of one color around the opposing king become weak. This is called a disaster. In both games, the Black king is prevented from castling in either direction by a crossfire from the unopposed White queen and bishop. Once he is stuck in the center, all that remains to be done is to open the center and let the rooks pour down the open files with devastating effect.

Notice in each game how no single move was a blunder. The weak square complex just sort of “appeared” all of a sudden, and then you just look at the position and say “Wow, this looks like trouble”. You have to develop a feel for weak squares. Two thoughts that can help are:

If you have traded off a bishop of one color, be careful about moving pawns to the other color.

If many of your pawns are already on one color, try not to trade off your bishop that guards the other color.

In other words, you have to take care to retain control of squares on your half of the board, especially the squares around your king. The two games presented illustrate Black violating both of these rules and being swiftly punished for doing so. Guard your squares and they will guard you!